Process of and apparatus for pickling metals



E. H. HINCKLEY.

PROCESS 0F AND APPARATUS FOR PICKLING METALS.

APPLICATION FILED IIIAY 2o, 1918.

1,434,011, Patented OCI. 31, I922.

-I HIIIIIIIUII Patented @et 3L @22 PROCESS F AND APPARATUS FR JPIECKLENG METALS.

.application filed May to,

To all wtom t may concern Be it known that l, Evnnn'rr lil. HINCnLnr, a lcitizen of the United States; residing at New Bedford, county'of Bristol, State of ll/lassachusetts, have invented an improvement in. ljrocesses'oi and Apparatus for Pickling Metals, of which the following description, in connection with the accompanying drawing, is a specication, like characters on the drawing representing like parts. l

Thisinvention relates to a process of and apparatus for icliling or treating metals with acid. While the principles oi the invention are ol broad application involving the treatmentoi various metals with various acids the invention ispeculiarly valuable in connection with the pickling of iron or steel articles to remove the scale therefrom such as occurs after annealing.

@ne object of the invention is to minimize the loss of the metal in the piclrling operation, the present invention in the case oi the piclrling of iron or steel articles resulting in a saving ot' over one-halt oit the iron lost in the pickling operation in those processes in general commercial use.

Another object or' the invention is to ei"- ect a saving in the acid employed, the present invention resulting in a large saving in this respect because ol the high efliciency of ionization at which the process is carried on.

Another object oi the invention is to enable the salt oi the metals produced, as for example ferrous sulphate or copperas when iron is pickled with sulphuric acid, to be so concentrated that when the piclrling liquor is cooled a large proportion is crystallized and can thus be recovered for commercial purposes without the more tedious and expensive process ci evaporation.

Another object of the invention is to en able the supernatant solution at the end ot the piclrling operation to be of such a character that it may be drawn oil3 and used over again in further pickling operations, the invention enabling this to be done because of the increase in the activity of the solution brought about.

The invention in its main. features 'resides in immersing the metalk such as iron in a solution of water and acid' such as sulphuric acid ol such a degree ot concen tration and raised to and maintained at such a temperature that .maximum eciency 119113. Serial lilo. Edlill;

of ionization and vthat maximum capacity for absorbin the salt produced as ferrous sulphate which arel simultaneously obtainable are thereby secured.

The objects and nature ot the invention wlll appear more fully from the accompanying description and'drawings and will be particularly ypointed out in the claims.

rlhe single ligure of drawing shows'more or less diagrammatically a simple and preierred iorm oil apparatus embodyin theinvention and by the use of which t e procp'ss mbodying the invention may be pracice The process and apparatus are particularly useful in connection with the piclrling of iron or steel articles such for example as .the'comparatively thin plates from which nails or tacks are produced and for convenience or disclosing the invention will be described in connection therewith, but 1t is to be understood that it is equally applicable to the treatment oi other metals with other acids. v

rlhe invention is based upon securing and correlating a proper degree ci" concentration in the acld solution and a temperature of that solution during the piclrling operation which will secure the most elhcient or most active ionization of the acid which can be obtained 'simultaneously with the greatest capacity or this solution for absorbing the salt produced; in other words7 the idea ot this invention is to secure that maximum etliciency of operation and that maximum capacity ot product which it is possible to secure simultaneously. :it will be obvious also thatthe invention may be substantially secured without reaching this maximum of perfection and a reasonable variation in either direction is considered as coming7 within the scope of the invention.

The efficiency of the ionization of the acid solution increases as the concentration of the solution decreases. Sulphuric acid, for example, atits strong commercial strength oi' about 96% is so lled with molecular H2504, that practically no ionization can talre place. Under the practice now commonly prevailing a solution of about is commonly employed which lat a temperature oi about C. permits oli approximately 23% of ionization or in other words approximately 23% oi'the H2504 molecules in the solution are in the form ot ione: This percentage of ionization inl y nanou v its 'solution also acts to increase the ionization in proportion to the increase in the volume caused thereby and in proportion to the in creased heat content of the ions.

While the efiiciency of ionization thus rapidly increases as vthe concentration of the solution decreases it will be seen that the capacity of the operation is reduced. For example, if the solution should be so decreased in concentration as to result in complete ionization of the acid the capacity of the operation would be very slight and the product of the ickling operation would be practically not ing but all acid present would be utilized'.

The capacity of the operation is determined by the amount of the salt roduced, in this case ferrous sulphate FeS 4, which can be absorbed by or go into solution in the solution. v-

It has been found that for practically any degree of concentration of the solut1on a temperature of 90 C. produces a condition in which FeSO4 has its maximum solubility and the temperature at which other salts have their maximum solubility and other acids their most efficient ionization may readily be determined by experiment.

The increase of temperature of the solution also acts to decrease the solubility of the solution for hydrogen gas and as hydrogen gas results from the union of the hydrogen ions produced in ionization and is freed it follows that the raisin of the temperature in this way also ena les the production of'further FeSO,t and thus increases the efficiency and capacity of the operation.

There is therefore a oint at which a certain concentration of t e solution raised to and maintained at a certain temperature will produce the maximum ionization and the maximum amount of salt, that is, the point at which the greatest efficiency and greatest capacity' that can be simultaneously obtained are in fact obtained.

In the case of the pickling of iron with sulphuric acid this is found to be when the sulphuric acid solution is at substantially one-half percent concentration and when the temperature is at substantially 90O C. Any substantial variation either in the degree of concentration or in the temperature either reduces both the efficiency and capacity of the operation or increases the one at the expense of the other with a total loss in each case.

This process it will be seen prevents any danger of the crystallization of the salt upon the article to be pickled because the schrtion can never reach such a de ree of cond centration that the salt will ge produced more rapidly than it can be dissolved by the solutlon. This condition has frequently obtained in commercial processes in practice and results in a super-saturated solution being formed locally around the article and a consequent crystallization of the salt upon the article which insulates it from the action of the acid and destroys or materially hinders the pickling' operation. v, This process also by maintaining an even and constant action of the' solution, prevents the solution from becoming dead as frequently happens in present commercial practice due to the oxidization of the ferrous to the ferric ion.

In the drawings there is illustrated a simple and preferred form of apparatus by which the process of this invention may be carried, on. As shown the articles to be pickled are iron plates l such as employed in the manufacture of tacks and nails. These plates are suitably supported on edge and held separated from each other by a suitable skeleton frame 2 which by means of supporting chains 3 may be handled from a crane or derrick. The frame 2 is made of bronze or other. material not subject to the action of the pickling solution.

A vat 4 of a size suitable to receive and (over the frame 2 with its supported plates 1 is provided. This vat is provided with means by which it may be filled with water and with means by which an amount of acid may be automatically supplied thereto to give the required concentration of solu tion in quantities sufficient to pickle the quantity of plates or articles carried by the frame. t

The amount of acid supplied to the solution may be automatically determined by a variet of means one form of which is herein ilustrated as a tank 5 to which a pipe 6 leads from a suitable source of acid supply. The flow from the pipe 6 is controlled -by a valve 7 operated by a float 8. The tank 5 discharges into the vat 4 through the pipe 9 the upper end of which is provided with a siphon valve 10 raised by a connection 11 to a trip lever 12 located in the descending path of the frame 2. This is so arranged that as the frame 2 is lowered into the vat 4 i't strikes the trip lever 12 and as a result discharges the contents of the tank 5 into th'e vat 4. This general type of means for discharging a predetermined quantity of liquid from the tank 5 into the vat 4 is shown in the patent to Craigie No. 433,447 granted August 5, 1890, It will thus be seen that by a simple calculation based upon the surface area of the articles 1 to be pickled, the contents of the tank 5 discharged upon the raising of the siphon valve l0, the strength of the acid in the tank 5,

incanti and the quantity of water in the -vat d, that the degree ot convcentration of the solution produced in the lvat t may be automatically and accurately secured.

The desired temperature of the solution in the vat 4 may be obtained in any suitable manner and for that purpose a steam pipe 13 connected to a suitable source ot steam supply la extends into the vat a and opens near the bottom thereofAv A. thermostatically controlled valve 15 is provided in the pipeA 13. This valve is ot a familiar type operated by a thermostat -16 containing an expansible liquid which in turn' operates through a flexible connection 17 the mov Aable parts of the valve W hen this thermostat is set to operate at a desired temper-V ature as, for example, 90 C., it will auto matic-ally act by the opening and closingv fot the valve 15 to supply the steam necessary to raise the solution to and maintain it 'at the desired temperature. llt is found that the condensate from the steam pipe will in practice about equal the evaporation so that this means of maintaining the temperature has no appreciable leffect upon the degree of concentration of the solution.

l. At the conclusion ot the piclrling oper-ation practiced in accordance with this invention the resultant solution will be tound to be of such a high degree of concentration that when it is cooled a large proportion ot the salt produced such as ferrous sulphate will crystallize and may be recovered for commercial purposes simply by drawing oil the supernatant liquorn This is a very val uable feature of the process because heretofore the general practicehas been to secure the salt by evaporation which requires time and is expensive. A. further valuable teature is due tothe fact that the salt crystallizes spontaneously and gradually and is therefore recovered in a more chemically pure state.

Furthermore, the supernatant liquor itself is a solution ci sulphuric acid and water and uncrystallized ferrous sulphate and is not only oi sucient strength but in tact of greater stren h than is necessary `tor use in continuing t' e future pickling operations. This is due to the decreased concentration of the S0)4 ion; that isto say, in this solution the S04 ion exists in small numbers so as not to oppose'the decomposition ot molecular sulphuric acid into its ions.

The supernatant liquor is therefore drawn ed into another vat and by the addition ot the proper amounts ot water and fresh sulphuric acid brought to the desired degree of concentration. This may be done in various ways. f

Tn the drawings a second vat 18 is located adjacent the vat 4 and connected thereto by a pipe 19 provided with valves 20 and 21. Between these valves a pipe 22 is connected to the pipe 19 and extends to a steam injector 23 connected to the source of steam supply 1a. At the conclusion of the pickling operation in the vat 4 andafter the solution therein has cooled the valve 20 is opened, the valve 21 being closed, and steam is turned on by the valve 24 thus injecting the supernatant liquor in the vat t into the `vat 18.

Then the required amount of water and acid from a second tank 25 is introduced into the vat 18' to bring the solution up to the required degree 'ot' concentration as one- \halt of one percent. The valve 2t is then closed and the pipe 13 swung over into the vat 18 and the thermostat ldplaced in the vat 18 whereupon the vat 18 is ready for a second piclrling operation.

At the conclusion ot this piclrling opera tion theinjector 23 is swung over into the vat d and the vsupernatantliquor drawn from the vat 18 into the vat d' in a manner similar to that just described. Thus by means of an yapparatus such as that disclosed the piclrling operation may be carried on indefinitely.

The process of applyin the vsolution to the metal has been reterre "to herein as that ot immersion but it is to be understood that this term is to be taken as including any process by which the solution is applied so as to cover the surface of the metal to be acted upon. Y

'Having fully described my invention, what l c aim as new and desire to secure by Letters Patent is:

1. The process of piclrling iron which consists in immersing the iron in a solution of water and sulphuric acid of such a degree ot concentration and raised to and maintained at such a temperature that that maxi mum emciency ot ionization and that maximum capacity tor absorbing ferrous sulphate which are simultaneously obtainable are thereby secured..

. 2. The process oi piclrling iron which consists in iersing the ironin a solution ci? water and suantially one-halt of one pers cent of sulphuric acid and raisin the solu= tion to an maintaining it at su stantially 90 C. whereby substantially that maximum degree of eciency or ionization and substantially that maximum capacity for absorbing ferrous sulphate which are simultaneously obtainable are thereby secured.

d. Tnthe process of piclrling iron in a solution of water and sulphuric acid the step which consists in maintaining said solution at a'temperature ot approximately' 90 C.

4r. The process ot piclrling metal which consists in immersing the metal in a solution of water and acid and in maintaining the concentration of the solution at or below that point at which all the salt produced will be dissolved by the solution.

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The process of pickling metal which consists in immersing the metal in a solution of water and acid and in maintaining the solution at such a temperature and at such a degree of concentration that the maximum number of hydrogen ions which can be economically utilized are formed in the solution. 6. The process of pickling metal defined in claiml 1 together with the additional steps of allowing the solution to cool at the end of the pickling opera-tion, removing the supernatant liquid, adding thereto amounts of water and acid de endent upon' the .surface area of a secon batch of metal to be pickled suiiicient to give the required concentration of solution, immersing the second batch in the solution and maintaining the solutionat such a temperature that that maximum efficiency of ionization and that maximum ca acity for absorbing the salt produced w ich are simultaneously obtainable are thereby secured.

7. The process of pickling metal defined in claim 1 which consists in addition in allowing the solution to cool and thus permitting the salt produced to crystallize spontaneously and gradually thus producing a substantially chemically pure salt, and in removing the supernatant liquor.

8. An apparatus for pickling metal which consists in a vat adapted to contain the pickling solution, means for automatically supplying an amount of acid to said Vat sulficient to give a predetermined degree of concentration to the solution, and means for automatically maintaining the temperature of the solution at a predetermined point durinlg the pickling operation.

9. n apparatus for pickling metal which consists in a vat adapted to contain a pickling solution, means for automatically su plying an amount of acid to said vat su 11. The process of picliling metal which consists in immersing the metal in a solution of water and acid having a degree of concentration within such a range and raised to and maintained at a temperature within such a range that substantially the same proportion of salt will be crystallized out for any degree of concentration within said range provided the temperature within its range be inversely proportioned.

12. The process of pickling iron which consists in immersing iron in a solution of water and sulphuric acid having the concentration ranging from one half of one percent to ten percent of sul huric acid and raising the solution to an maintaining it at a temperature ranging from ninety degrees C. to seventy-five degrees C. according to the concentration whereby substantially the same proportion of ferrous sulphate will be crystallized out whatever be the degree of concentration within the range stated provided the temperature is inversely proportioned thereto within the range stated.

In testimony whereof, I have signed my name to this specification.

EVERETT H. HINCKLEY. 

